This invention relates to a high resolution observation apparatus with a photon scanning microscope for detecting evanescent light which depends on material features of a sample by irradiating light to the sample at a total reflection angle.
As shown in FIG. 2, a photon scanning microscope conventionally, for example as described in "Kougaku" Vol. 20, No. 3 p.p. 134-141, generates the light which is emitted from a semiconductor laser optical source 8 and which has a single wavelength to be incident to a prism 1 at a total reflection angle, and detects evanescent light which is emitted depending on the topography of a surface of a sample 2 on the prism 1 by an optical fiber probe 3 with a minute opening and an optical detecting system 10.
Then, the optical fiber probe 3 scans the sample in x and y-axis directions while controlling the z-axis direction so that the detected evanescent light should be constant, and the control signal and the scanning signals are processed, and thereby a three-dimentional shape of the sample surface is determined. Moreover, only light having the same wavelength as of the incident light that is detected.
However, the photon scanning microscope is conventionally used for observing the topography of the sample surface and the observation is performed with the precondition that the sample is scanned so that the detected evanescent light is constant and that the evanescent light depends on the distance between the sample surface and the probe tip.
Therefore, if the sample includes materials with different transparency or different refractive index from the rest of the sample, incorrect topography is observed. Moreover, it is essentially impossible to detect the difference in transparency or the difference in refractive index within the sample.
For example, in FIG. 3A, the sample 22 has a wave shape surface 22a and has an uniform optical constant, such as transparency or refraction index. In this case, when light 21 is incident to a prism 1 at a total reflection angle and an evanescent light emitted from the sample 2 by the incident light 21 is detected by an optical fiber tip 3, a locus 23 of the optical fiber tip results in a flat shape after scanning the optical fiber tip above the sample surface with controlling the z-axis direction so that the detected evanescent light is constant. The conventional photon scanning microscope, therefore, can not observe the sample surface 22a correctly if the sample has a uniform optical constant.
In another example shown in FIG. 3B, the sample 24 has a flat surface and has singular regions 24a which have a different optical constant, such as transparency or refraction index, from the remaining regions 24b of the sample 24. In this case, when light 21 is incident to a prism 1 at a total reflection angle as the same manner in the above example, a locus 25 of the optical fiber tip results in a wave shape after scanning the optical fiber tip because the singularity of the optical constant within the sample affects the evanescent light emitted by the incident light. The conventional photon scanning microscope can not observe the sample surface correctly, either, if the sample has some singular region of optical constants even if it has a flat surface.
Further, only the evanescent light emitted by the wavelength of the incident light is detected because the detected light has the same wavelength as that of the incident light. It is, therefore, impossible to observe fluorescent condition of the sample in other wavelength than that of the incident light.
Moreover, in a general optical observer, the resolution of observation is limited by optical diffraction limit. Namely, the resolution is at the same level as that of the wavelength of the incident light.